US 7980171 B2
A cooking or food warming appliance having a heated heat sink plate situated in a vacuum environment within an outer shell. A food vessel intimately engages the heat sink plate along a food contacting surface thereof by virtue of the vacuum. The vacuum eliminates air gaps between the food contacting surface of the food vessel and the heat sink plate so as to provide instantaneous and uniform heating of the food vessel. The vacuum environment also provides thermal insulation for the heat sink plate whereby heat loss by convection is virtually eliminated.
1. A cooking or warming appliance comprising:
a. an outer shell;
b. a food vessel having a cooking surface on an interior surface, said food vessel removably positioned within the outer shell and defining a space between an exterior surface of the food vessel and an interior surface of the outer shell when the food vessel is placed therein;
c. sealing means co-acting between the outer shell and the food vessel;
d. means for selectively activating and deactivating a vacuum condition in said space;
e. a metal heat sink plate positioned within said space, adapted to forcibly and uniformly contact the exterior surface of the food vessel beneath said cooking surface when the vacuum is activated;
f. electric heating means positioned within said space to heat said heat sink plate when the vacuum is activated; and
g. means for spacing said heat sink plate and heating means from the interior surface of the outer shell, whereby said vacuum condition when activated surrounds said heat sink plate and heating means within said outer shell to permit heat to pass only by conduction from the heat sink plate to said cooking surface.
2. The appliance of
3. The appliance of
4. The appliance of
5. The appliance of
6. The appliance of
7. A food cooking or warming appliance comprising:
a. an outer shell;
b. a heat sink plate positioned within the interior of the outer shell;
c. electric resistance heating means positioned within the shell associated with the heat sink plate for heating the plate to a desired temperature;
d. a removable food vessel for selective placement within the outer shell, said vessel having a food contacting surface for placement adjacent to said heat sink plate;
e. a lid adapted to selective engagement with one of the outer shell or the food vessel;
f. a vacuum pump means communicating with the interior of the outer shell to selectively create a vacuum around the heat sink plate and heating means, and between the outer shell and one of the removable food vessel or lid, wherein said vacuum pump means is selectively deactivated to permit removal of one of the food vessel or lid from the outer shell; and
g. a sealing means cooperating between one of the lid and the outer shell or between the food vessel and the outer shell.
8. The appliance of
9. The appliance of
10. The appliance of
11. The appliance of
12. A method of cooking or warming food comprising the steps of:
a. providing an outer shell;
b. providing a heat sink plate and electric heating means within the outer shell;
c. providing vacuum means for selectively providing a vacuum around the heat sink plate and the heating means;
d. providing a removable food vessel for placement in the outer shell whereby the food vessel forcibly and intimately contacts the heat sink plate, when the vacuum condition exists in a space between the food vessel and the outer shell, whereby the vacuum prevents heat loss through the outer shell;
e. providing removable lid means adapted to selectively fit the outer shell and the food vessel;
f. providing sealing means to selectively establish a vacuum tight seal between one of the lid and the outer shell during a preheating step and between the food vessel and the outer shell during a cooking or warming step; and
g. deactivating the vacuum means to permit selective removal of one of the lid means or food vessel from the outer shell after respective preheating and cooking or warming steps.
13. The method of
a. placing the lid on the outer shell to engage said sealing means;
b. activating the vacuum means to create a vacuum environment within an interior space defined by said outer shell and said lid;
c. energizing the heating means within the vacuum environment to obtain a desired preheat temperature and maintaining said temperature; and
d. deactivating the vacuum means to permit removal of the lid from the outer shell and placement of the cooking vessel in the outer shell.
14. The method of
a. placing the food vessel in the outer shell to engage said sealing means;
b. activating the vacuum means to create a vacuum environment within an interior space defined by said outer shell and said food vessel, said vacuum environment causing forcible and intimate engagement between the food vessel and the heating means as well as insulating said heating means from convection heat losses; and
c. deactivating the vacuum means to permit removal of the cooking vessel from the outer shell upon completion of the cooking step.
15. The appliance of
This application is a continuation-in-part of co-pending U.S. application Ser. No. 11/245,478 filed Oct. 6, 2005, and is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates generally to electric cooking appliances and, more particularly, to an electric cooking or food warming appliance having a thin food contacting surface, preferably of stainless steel, that intimately engages a thicker heat conductive core or heat sink plate of copper or aluminum by means of a vacuum to maximize heating uniformity and minimize heat loss.
2. Description of Related Art
Briefly stated, the invention disclosed in parent application Ser. No. 11/245,478 is directed to a composite griddle plate comprising a core consisting of a metal plate having a high coefficient of thermal conductivity such as copper or aluminum. The core plate is faced at least with an upper sheet of a metal such as stainless steel or titanium which defines the cook surface of the griddle plate. The interface between the core plate and upper sheet is under the reduced pressure of a vacuum so as to cause intimate contact between the core and cook surface which increases the thermal conductivity to the cook surface and, thus, reduces the thermal recovery time of the griddle.
Various additional embodiments of the original invention are also disclosed in the parent application. For example, the griddle plate of one such embodiment comprises a high heat conductivity core of copper or aluminum having upper and lower sheets of stainless steel in intimate contact with the core. The entire perimeter of the griddle plate is sealed as by welding and the interior is under a permanently sealed vacuum. Another such embodiment utilizes an upper sheet of stainless steel or other metal having a non-stick coating applied thereto. The upper sheet is removably secured to the heat conductive core plate under vacuum utilizing a high temperature gasket or adhesive sealant to maintain the vacuum. The upper sheet may be mechanically secured by bolts or the construction may be placed under a constant vacuum using a vacuum pump. When the non-stick surface ages and/or otherwise loses its non-stick properties, such as with a PTFE-type non-stick coating, the upper sheet can be easily replaced with a freshly non-stick coated upper sheet and the vacuum reestablished.
The present invention incorporates several aspects of the invention disclosed in parent application Ser. No. 11/245,478, namely, the attachment of a thin metal cook surface to a thicker core layer or heat sink by way of a vacuum to ensure uniform surface contact between the cook surface and the heat sink which provides instant heating as well as uniform heating over the entire cook surface. The subject parent application also discloses the removability of the cook surface from the heat sink through the use of a vacuum pump and high temperature gasket sealing around the perimeter of the cooking surface. The removability feature is particularly beneficial when a non-stick PTFE type surface is present on the cook surface since it permits periodic replacement of the cook surface and its non-stick surface.
Briefly stated, a presently preferred embodiment of the present invention comprises a heat sink plate with heating means associated therewith. The heat sink is surrounded by a vacuum when in use so as to provide a heat insulating environment for the heat sink so as to minimize heat loss and maximize energy efficiency. A food vessel tightly engages the heat sink along the cook surface thereof by virtue of the vacuum. In preferred embodiments, the invention contemplates that the heat sink is enclosed by a metal pot-shaped shell which communicates with a vacuum pump. The invention includes sealing means to contain the vacuum between the shell and the food vessel.
The food vessel is removable from vacuum engagement with the shell and heat sink to permit easy cleaning thereof. When the food vessel is so removed, the heat sink may be preheated or maintained at temperature under vacuum through the use of a lid which engages the sealing means and maintains the vacuum within the shell and around the heat sink. When the food vessel is prepared and loaded with ingredients for cooking, the vacuum is halted to permit removal of the lid and insertion of the food vessel in the shell. The vacuum is again established around the heat sink for heat insulation of the heat sink and for tight engagement between the heat sink and the cook surface of the food vessel.
Food preparation with an electrical cooking device represents certain advantages such as portability and versatility, and certain drawbacks such as lack of ease of cleaning, evenness of heating, and safety. The present invention provides an electrical cooking apparatus with unique features in construction and performance that addresses the shortcomings of the traditional electrical cooking apparatus. The central feature of this appliance is the use of vacuum as both an insulator and as a means of attaching the cooking vessel to the heat source.
The vacuum cooking appliance 10 shown in
A vacuum is created in the interior space 30 defined between the outer shell 12 and the food vessel 14 by the vacuum pump 32. The high temperature seal 24 is somewhat compressible which allows the bottom wall or cook surface 15 of the food vessel 14 to come into intimate contact with the heat sink 16 as vacuum builds in space 30. The heat sink 16 is a thicker plate of metal (copper, aluminum, steel, etc.) which is intended to store latent energy from the resistance heater 20, then deliver that energy in a rapid and even manner to the cook surface 15 of the food vessel 14. The mass of the heat sink plate 16 is adjusted to fit the application of the apparatus 10. The heat sink plate 16 is preferably one of aluminum or copper.
The temperature of the heat sink 16 is controlled by the thermostat 40 which has a probe connected directly to the heat sink or by means of a non-contact sensing device. The elements of the resistance heater 20 may be mechanically attached to the heat sink 16 or may be cast into the heat sink. The wattage of the resistance heaters is adjusted according to the application of the apparatus 10. The lid 50 is provided which securely fits the outer shell 12 as well as the food preparation vessel 14. During a pre-heat period, the lid 50 is placed on the high temperature gasket 24 without the food vessel placed in the outer shell. The vacuum pump 32 is turned on and the resulting vacuum that is developed in the interior space defined between the lid 50 and shell 12 insulates the heat sink plate 16 during the heat-up period. To start the cooking cycle, the solenoid 42 opens and vents the evacuated space between the outer shell 12 and lid 50 so that the lid may be removed and the food vessel 14 put in place inside the shell 12. The vacuum switch 44 turns on the vacuum pump 32 and the thermostat 40 turns on the resistance heaters 20 as energy flows to the food vessel. The legs 18 which support the heat sink 16 provide a spaced gap between the bottom of the heat sink 16 and the outer shell 12. The height of the legs is adjusted to place the heat sink 16 in contact with the surface 15 of the vessel 14 so as to provide maximum clamping force between the food vessel 14 and heat sink 16 when the vacuum is applied. This great clamping force is possible by virtue of the fact that the space 30 is under vacuum while the space above the food vessel is at atmosphere. The resultant net force acting to press the surface 15 against the heat sink 16 may be well in excess of 1,000 pounds. The lid 50 which was used to maintain the vacuum during the pre-heat period fits the food vessel 14 and can be used as a lid during the cooking cycle.
The food vessel 14 can be made from a food grade material such as stainless steel or a less expensive material which is coated with a synthetic material such as a PTFE (non-stick). A multi-ply bonded material of stainless steel-aluminum-stainless steel, for example, would also be useful as a material for the food vessel 14 to promote heat flow to the vessel and to conduct heat throughout the vessel.
The wires to the resistance heater 20 and the thermostat 40 must pass through the outer shell 12, such as through port 36, without allowing loss of vacuum. This is accomplished through the use of appropriate gaskets and sealants. The vacuum port 36 to the outer shell can also double as the entry point for these wires to minimize the number of possible vacuum leakage points in the outer shell 12. Energy consumption is minimized by the design of the apparatus as outlined below.
A. Convection loss is minimized by the evacuation of the space 30 surrounding the heat sink 16 during the heat-up period. Convection loss is minimized during the cooking cycle by reestablishing the vacuum after the lid has been removed and the food vessel 14 has been put in place in a sealed relationship at gasket 24 with the outer shell 12.
B. Conduction losses are minimized by using a low conductivity material for the heat sink support legs 18 such as stainless steel or ceramics to space the heat sink plate 16 from the shell 12. Also, the contact points for the legs 18 are kept to a minimum. Hence, loss of heat by conduction from the heat sink plate 16 to the shell 12 is minimized.
C. Radiant losses are minimized by providing a smooth reflective surface for the heat sink 16, the interior and the exterior of the outer shell 12.
With the food vessel 14 removed from the outer shell 12, the lid 50 is placed on the vacuum seal 24 that is located at the top flange of the outer shell 12. The apparatus 10 is turned on and the lid 50 is drawn down by the differential between the atmospheric pressure outside the lid and the vacuum beneath the lid, and the heat sink 16 begins to heat by virtue of the resistance heater 20. When the apparatus has achieved the pre-set vacuum level (approximately 23 inches of mercury) and the desired pre-set temperature, both the vacuum pump 32 and resistance heater 20 turn off. When desired, the operator switches the solenoid valve 42 which vents the evacuated space between the food vessel and the outer shell to atmosphere to free the lid. The lid is removed from the outer shell and the food vessel 14 with the food to be cooked thereon is placed inside the outer shell 12 with the upper flange of the food vessel 14 resting on the high temperature seal 24. Vacuum is reestablished and a tight clamping force is generated between the cook surface 15 of the food vessel 14 and the heat sink 16. When the cooking cycle is finished, the food vessel 14 is removed and the unit is either turned off or the lid is replaced on the vacuum seal to maintain the heat in the heat sink 16.
Among the advantages provided by the present invention are the following:
A. Preheat—The time to preheat is separate from the cooking cycle. The apparatus can be left turned on and ready to cook but in an idle mode that is consuming little energy because the heat sink is surrounded by a vacuum.
B. Even Heating—The heat delivered to the cook surface 15 of the food vessel 14 is completely evenly distributed throughout the heat sink 16. The high clamping force of atmospheric pressure eliminates air gaps between the heat sink 16 and the cook surface 15 to thus assure well distributed delivery of the latent energy in the heat sink to the cook surface.
C. Speed—The delivery of heat energy to the cook surface 15 of the food vessel 14 is instantaneous.
D. Accuracy—The thermostatically controlled heater 20 in the heat sink 20 delivers no more and no less than the desired temperature.
E. Easy Cleaning—The detachable food vessel 14 is easily removed for cleaning.
F. Simplicity—The technology of the apparatus is very simple and involves no complicated electronics.
G. Energy Efficiency—The design of this apparatus minimizes consumption of energy. When cooking, the energy yielded from the heat sink is conducted straight to the food being processed.
H. Safety—When used in a situation such as a buffet serving dish, there is no hot water or fuel container to present a safety hazard. There are no high frequency electromagnetic waves that could affect biomedical devices.
An apparatus 10, as depicted in
The apparatus depicted in
As shown in
Two outer shells (not shown, but similar in concept to shell 16) are attached by a hinge in a “clam shell” type of arrangement. Both halves are equipped with a heat sink 16 and a port 36 to a vacuum pump 32. When the two halves are closed on each other, high temperature seals 24 around the perimeter of each shell contact the other. In other words, the clam shell is closed and the vacuum seal of each half contacts the other half. Vacuum is established and the heat sinks 16 in each half are preheated to a desired temperature. When desired, the vacuum is vented to atmosphere and the claim shell is opened. Grill vessel plates 14 which may include cast aluminum with a non-stick coating are placed against the vacuum seals 24 and vacuum is established in each of the two halves. When the clam shell is closed again, it may be used as a waffle maker, a two-sided grill, a panini press, or any other two-sided heat source application. The usage is determined by the plates or sheets 14 which are vacuum attached to the heat sinks 16 within the outer shells 12.
This example is similar to Example 1, however, the outer shell 16, food preparation vessel 14 and lid 50 may be shaped in a rectangular configuration (in plan view) to assume the general size and configuration of a commercial warming tray or chafing dish. In such commercial settings, it is important to maintain the already cooked food at a holding/serving temperature between about 167° F.-185° F. This temperature range is of importance because bacteria will grow at temperatures below 167° F. and cooking will continue at temperatures above 185° F. The operation of the food warming device of this example is the same as that set forth in the previous examples except that the temperature of the heat sink plate is maintained between 167° F.-185° F. so that precooked food placed in the food vessel 14 remains at a safe temperature during holding/serving without being overcooked.